A pregnant woman at 28 weeks is screened for gestational diabetes mellitus (GDM) with a 75g OGTT (IADPSG/WHO criteria). Her results are: fasting 90 mg/dL, 1-hour 185 mg/dL, 2-hour 155 mg/dL. Does she have GDM, and what does the HAPO trial evidence underlying these thresholds demonstrate?

• A She does NOT have GDM — all values are below the IADPSG thresholds (fasting ≥92, 1-hr ≥180, 2-hr ≥153 mg/dL); only one value needs to be met or exceeded for diagnosis
• B She DOES have GDM based on 1-hour value ≥180 mg/dL alone being the diagnostic criterion
• C She DOES have GDM — 1-hour ≥180 mg/dL and 2-hour ≥153 mg/dL both meet IADPSG criteria; only ONE value needs to be met for diagnosis ✓
• D She does NOT have GDM because the diagnosis requires all three values to be elevated simultaneously

Explanation

IADPSG/WHO 2013 diagnostic thresholds for GDM with 75g OGTT: fasting ≥92 mg/dL, 1-hour ≥180 mg/dL, 2-hour ≥153 mg/dL. Diagnosis is made when ANY ONE or more values meet or exceed the thresholds. This patient has 1-hour 185 mg/dL (≥180) AND 2-hour 155 mg/dL (≥153) — both diagnostic. Fasting is 90 mg/dL (below 92, normal). HAPO study (Hyperglycemia and Adverse Pregnancy Outcomes) showed a continuous linear relationship between glucose levels and adverse outcomes (macrosomia, primary cesarean, neonatal hypoglycemia, cord C-peptide) establishing the IADPSG thresholds at odds ratios of 1.75 above mean glucose for each outcome.

Reference: Williams Obstetrics, 26th ed.

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Written and medically reviewed by the StethoPrep medical team.